1. Field of the Invention
The present invention relates to a recording apparatus.
2. Description of the Related Art
In addition to previously known video cameras for recording obtained image signals on magnetic tapes, video cameras for encoding obtained image signals and recording the encoded image signals in accordance with the MPEG (Moving Picture Experts Group) system have recently appeared on the market.
Typically, this type of video camera obtains and records an NTSC image signal of 60 fields per second. Another type of video camera has also appeared on the market. This type of video camera has the ability to convert an obtained image signal of 24 frames per second such as an image signal used for a movie into an image signal of 60 fields per second and record the converted image signal.
Thus, as a method of converting a film source such as a movie into an interlaced video signal, the 2-3 pulldown technique is widely used. That is, since film employs recording at 24 frames per second whereas videotape employs recording at 30 frames (60 fields) per second, number of fields conversion is performed using the 2-3 pulldown technique. More specifically, as shown in FIG. 1, number of fields conversion is performed by providing a redundant field (hereinafter referred to as a repeat field) every other frame.
A 2-3 pulled-down video signal has a repeat field every other frame, and therefore, a frame in which a top field is displayed first and a frame in which a bottom field is displayed first are interchanged every three frames.
On the other hand, if a typical interlaced video signal of 60 fields per second is recorded in accordance with the MPEG system, a top field (first field) and a second field are typically encoded as a single frame. Therefore, a top field is displayed first in all frames.
As shown in FIG. 2, the case in which MPEG data encoded using the 2-3 pulldown technique and MPEG data acquired by encoding a typical image signal of 60 fields per second are spliced and recorded on tape using a video camera will be considered. In this case, a field alternation error, where a top field is followed by a top field, can occur depending on the frames to be connected. Consequently, an image is sometimes distorted during playback thereof.
As a solution for the above-described case, a technique described in Japanese Patent Laid-Open No. 9-121360 (U.S. Pat. No. 5,771,357 that is a counterpart thereto) has been proposed. In Japanese Patent Laid-Open No. 9-121360, compression coding is performed on the basis of fields, and an encoding start field and an encoding end field are specified, whereby the splice recording of streams can be achieved.
In reality, however, as shown in FIG. 3, an apparatus described in Japanese Patent Laid-Open No. 9-121360 cannot splice MPEG data encoded using the 2-3 pulldown technique and MPEG data acquired by encoding a typical image signal of 60 fields per second and record the spliced MPEG data, because the sequence of top and bottom fields are specified on the basis of a coding sequence. Field skipping can occur at the point where the splice recording is performed.
Referring to FIG. 3, Top_field_first and Repeat_first_field are information added to the top of each frame included in an MPEG stream. Top_field_first is a flag indicating which of top and bottom fields is output first when a corresponding frame is displayed. When Top_field_first indicates one, the top field is displayed first. When Top_field_first indicates zero, the bottom field is displayed first.
When Repeat_first_field indicates one, a field displayed first in a frame is displayed again in the same frame. When Repeat_first_field indicates zero, the top field and the bottom field are individually displayed in a frame.
As shown in FIG. 4, since there are no rules about a repeat field, a decoding time that does not normally occur, occurs at a splice point. In an area 401, even if the area is a typical 60-field interlaced part, a decoding time corresponding to a three-field period is required. As a result, such a stream format tends to cause various problems when it is encoded and decoded.
Accordingly, it would be desirable to provide a format that does not allow the aforementioned splicing anomaly to occur.